As mobile devices such as portable telephones are spread in recent years, memories used in these mobile devices are required to have lower current dissipation.
NAND flash memories are widely used in these mobile devices. It is extremely important to reduce the operation current of the NAND flash memories.
On the other hand, in “read”, “write (program)” and “erase” which are basic operations of the NAND flash memories, various boosted voltages (voltages generated in the memory which are higher than the power supply voltage supplied to the memory) generated by a boosting circuit are used.
For securing the reliability, therefore, a plurality of boosting circuits which supply various voltages are needed. As a result, the current consumption of the NAND flash memory is increased.
In some conventional boosting circuits, the number of boosting stages is changed over by a switch and boosted voltages of two kinds are output (see, for example, JP-A-2004-348806 (KOKAI)).
However, specific description concerning a clock signal which causes a pump in each boosting stage in the conventional boosting circuit to operate is not found, and study about the pump efficiency, i.e., the current dissipation is not conducted.